Three instruments, three kinds of information
Pace describes external work. Heart rate describes part of your internal response. Perceived effort describes how the session feels. They often move together, but heat, hills, dehydration, poor sleep, stress and accumulated fatigue can separate them.
The formula is not your measured maximum
Age-based maximum-heart-rate equations estimate the average for a group. An individual can sit meaningfully above or below that average. Wrist sensors can also lag or misread during movement, while some medicines change heart-rate response.
Use a cross-check
For an easy session, compare heart rate with breathing and the talk test instead of chasing one exact beat. Stop for chest pain, fainting, an irregular heartbeat or unusual shortness of breath. People with heart conditions, pregnancy, activity restrictions or medicines that affect heart rate should ask a qualified professional for individualized limits.